Jurors have cleared the former operator of a northwestern Indiana wastewater treatment plant and two of its employees of charges that they tampered with tests in violation of the federal Clean Water Act.

Jurors reached the verdict Friday after hearing nine days of testimony over whether New Jersey-based United Water Services and the staffers would raise chlorine levels at the Gary wastewater treatment plant just before testing for E. coli, then lower the chlorine to insufficient amounts to kill the bacteria.

Federal prosecutors filed the charges in 2010, saying the company used lower chlorine levels from 2003 to 2008 to save money.

United Water CEO Bertrand Camus said in a statement the company always believed it would be exonerated and that it met environmental standards at the Gary treatment plant.